1. Technical Field
This invention relates to the field of continually variable transmissions that produce a stepless, continually variable range of speed ratios. More particularly, the invention pertains to a compact arrangement of such a transmission having fixed ratio and variable ratio drive mechanisms.
2. Description of the Prior Art
Automatic transmissions for automotive use that employ a belt drive, variable speed ratio mechanism, usually include a torque converter located in the driveline between the power source and the continually variable drive mechanism. At the lower speed ratios, the torque converter produces torque multiplication to assist accelerating the vehicle from rest. At higher speed ratios, the torque converter is locked up to produce a mechanical connection between its input and output, rather than the conventional hydrodynamic connection, to minimize losses inherent in its operation. At higher speed ratios, the belt drive mechanism alone produces the torque multiplication and speed reduction between the power source and drive wheels. However, in conventional continually variable transmission arrangements, acceleration of the vehicle from rest is only marginally acceptable when compared to current four-speed automatic transmission in current use.
In the design of continually variable transmissions, there is a long felt need to extend as much as practicable the range of speed ratios that can be produced by the belt drive mechanism and to minimize the torsional loads on the belt drive mechanism. Furthermore, it is known that in conventional continually variable transmissions that include a torque converter, the pumping losses during low speed operation, particularly when accelerating the vehicle from rest, are high, due to high clamping loads between the sheaves of the belt drive mechanism and the belt itself.
Copending patent application Ser. No. 08/697,964 describes an arrangement to address the above concerns, but which is difficult to package in small spaces. The present invention seeks to improve the package size of a dual mode CVT.